1. Field of the Invention
This invention relates to acrylic copolymers with very few impurities and the compositions thereof. The compositions of the acrylic copolymer are applicable onto the surface of the skin and form a very thin but strong film. The skin protective compositions are less irritative to the skin because they contain no surfactants. The thin film, once formed, is resistant to an acidic or neutral environment but easily dissolved in a slightly alkaline environment. In other words, the film is easily washed away by lathering with a toilet soap and water.
2. Prior Arts
Coating compositions which guard the skin from injury by chemicals or other irritants are known. They are designed to protect the skin by a thin film formed on the skin.
Traditionally, cellulose derivatives dissolved in a strong organic solvent such as acetone and ethyl acetate were used, which held such problems that the organic solvent irritated the skin or the mucosa, and that the formed coat film could not be removed easily from the skin.
Recently, a skin protective composed of n-butyl polyester/maleic acid and plasticized ethyl cellulose as main components (hereinafter, sometimes called the protective depending on the prior art) is commercially available in the U.S., but it is not allowed yet in practical use in Japan because it includes some problems in use in that its safety has not been proven.
This protective coating, depending on the prior art, forms a protective film between the skin and extracorporeal catheter, adhesive tape, plaster, diaper or the like. Also, such a usage as to protect the hands from being soiled with grease has been proposed.
The present inventors have strenuously investigated for such a polymer capable of covering the skin of housewives and dishwashers in a restaurant, hospital and a beauty salon who use neutral detergents. Acrylic copolymers have long been practically used in the medical field and are known to have a high safety. But since all the existing acrylic copolymers are manufactured in a routine polymerization, such as solution polymerization and emulsion polymerization, those copolymers are rich in anionic surfactants, chain transfer agents and residual monomers. Accordingly not only are they irritative to the skin and, and introduce problems in environmental protection, but also the coat films become brittle and exhibit waterproof properties when a surfactant exists therein. Hence, these polymers are not suitable in the present invention which aims at providing a film which is impermeable to neutral detergents.
On the other hand, the study of a method to synthesize a copolymer emulsion without using a water-solubilizing agent, such as a surfactant or the equivalent has been continued, but it has been reported that, in the case of polymerizing ethyl acrylate and acrylic acid, for example, that when the quantity of acrylic acid exceeds 2 to 3 molar percent, the formed copolymer emulsion becomes mechanically unstable, which tends to induce gelation (Matsumoto et al.; Kobunshi Ronbunshu, vol. 32, No. 9, 1975).
Moreover, it was made clear that acrylic copolymers already known for pharmaceutical use, for example, represented by Eudragit.RTM. made by R/e,uml/o/ hm Pharma, West Germany, that these copolymers suffer from defects in the elongation and tensile strength.